Photo transistor and display device including the same

ABSTRACT

A photo transistor and a display device employing the photo transistor are provided. The photo transistor includes a gate electrode disposed on a substrate, a gate insulating layer that electrically insulates the gate electrode, a first active layer overlapping the gate electrode and including metal oxide, wherein the gate insulating layer is disposed between the gate electrode and the active layer, a second active layer disposed on the first active layer and including selenium, and a source electrode and a drain electrode respectively electrically connected to the second active layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and benefits of Korean PatentApplication No. 10-2019-0174429 under 35 U.S.C. § 119, filed in theKorean Intellectual Property Office on Dec. 24, 2019, the entirecontents of which are incorporated herein by reference.

BACKGROUND 1. Technical Field

The disclosure relates to a photo transistor and a display deviceincluding the same.

2. Description of the Related Art

A photo transistor may be a type of optical sensor that may convertlight energy into electrical energy. A photo transistor may utilize aphotovoltaic effect in which a current flowing according to theintensity of light changes. A photo transistor has an advantage of beingmore sensitive to light than a photo diode because a photo transistorcan amplify the photocurrent using a transistor.

Since an oxide semiconductor may have various advantages over amorphoussilicon, such as high mobility, transparency, and a low temperatureprocess, efforts have recently been made to utilize an oxidesemiconductor for a photo transistor.

It is to be understood that this background of the technology sectionis, in part, intended to provide useful background for understanding thetechnology. However, this background of the technology section may alsoinclude ideas, concepts, or recognitions that were not part of what wasknown or appreciated by those skilled in the pertinent art prior to acorresponding effective filing date of the subject matter disclosedherein.

SUMMARY

Aspects of the disclosure may provide a photo transistor capable ofimproving a light absorption rate in a visible wavelength band.

Aspects of the disclosure may also provide a display device including aphoto transistor as an optical sensor.

However, aspects of the disclosure are not restricted to those set forthherein. The above and other aspects of the disclosure will become moreapparent to one of ordinary skill in the art to which the disclosurepertains by referencing the detailed description of the disclosure givenbelow.

A photo transistor according to an embodiment may include a secondactive layer including selenium in addition to the first active layerincluding metal oxide, thereby absorbing light (e.g., all light) in thevisible wavelength band. Thus, it may be possible to improve lightsensing characteristics. Further, it may be possible to improve thephotoresponsibity, photosensitivity and detectivity of the phototransistor.

A display device according to an embodiment may include a phototransistor having excellent characteristics, thereby improving the lightsensing characteristics of the display device.

The effects of the disclosure are not limited to the aforementionedeffects, and various other effects are included in the specification.

In an embodiment, a photo transistor may include a gate electrodedisposed on a substrate, a gate insulating layer that electricallyinsulates the gate electrode, a first active layer overlapping the gateelectrode and including metal oxide, wherein the gate insulating layermay be disposed between the gate electrode and the first active layer, asecond active layer disposed on the first active layer and includingselenium, and a source electrode and a drain electrode respectivelyelectrically connected to the second active layer.

In an embodiment, the first active layer and the second active layer maybe in contact with each other in a region in which the first activelayer and the second active layer overlap the gate electrode.

In an embodiment, the first active layer may be disposed closer to thegate electrode than the second active layer.

In an embodiment, the source electrode may cover a portion of the secondactive layer, and the drain electrode may cover another portion of thesecond active layer.

In an embodiment, a side edge of the first active layer and a side edgeof the second active layer may be in contact with each other and alignedwith each other.

In an embodiment, the source electrode and the drain electrode may bedisposed between the first active layer and the second active layer.

In an embodiment, the first active layer may include at least oneselected from an oxide semiconductor, amorphous silicon, polycrystallinesilicon, and a two-dimensional (2D) material.

In an embodiment, the oxide semiconductor may include a compound havingat least one selected from the group consisting of indium (In), zinc(Zn), gallium (Ga), tin (Sn), titanium (Ti), aluminum (Al), hafnium(Hf), zirconium (Zr) and magnesium (Mg), and the 2D material may includegraphene or MoS.

In an embodiment, the second active layer includes may include acompound having at least one of copper (Cu), indium (In), and gallium(Ga).

In an embodiment, the second active layer may have a thickness of about5 nm to about 300 nm.

In an embodiment, a display device may include a substrate including atransmissive region and a light emission region, a transistor layerdisposed on the substrate and including a first transistor and a secondtransistor, a light emitting element layer disposed on the transistorlayer and including a first electrode, and a touch sensor disposed onthe light emitting element layer and including electrodes. The firsttransistor may include a gate electrode, a first active layer includingmetal oxide, a second active layer including selenium, and source anddrain electrodes.

In an embodiment, the first transistor may overlap the transmissiveregion of the substrate, and the second transistor may overlap the lightemission region of the substrate.

In an embodiment, the first transistor may not overlap the firstelectrode of the light emitting element layer and may not overlap theelectrodes of the touch sensor.

In an embodiment, the second transistor may overlap the first electrodeof the light emitting element layer and may not overlap the electrodesof the touch sensor.

In an embodiment, the light emitting element layer may further include asecond electrode facing the first electrode, and an organic lightemitting layer disposed between the first electrode and the secondelectrode. The first transistor and the second transistor may overlapthe second electrode.

In an embodiment, the display device may further include a thin filmencapsulation layer disposed between the light emitting element layerand the touch sensor.

In an embodiment, the electrodes of the touch sensor include drivingelectrodes and sensing electrodes.

In an embodiment, the first active layer and the second active layer maybe in contact with each other in a region in which the first activelayer and the second active layer overlap the gate electrode.

In an embodiment, the first active layer may be disposed closer to thegate electrode than the second active layer.

In an embodiment, the second active layer may include a compound havingat least one of copper (Cu), indium (In), and gallium (Ga).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the disclosure will becomemore apparent by describing in detail embodiments thereof with referenceto the attached drawings, in which:

FIG. 1 is a schematic perspective view illustrating a photo transistoraccording to an embodiment;

FIG. 2 is a schematic cross-sectional view illustrating a phototransistor according to an embodiment;

FIG. 3 is a schematic cross-sectional view illustrating a phototransistor according to another embodiment;

FIGS. 4 to 8 are schematic cross-sectional views for describing a methodof manufacturing the photo transistor of FIG. 2 according to anembodiment;

FIGS. 9 to 11 are schematic cross-sectional views for describing amethod of manufacturing the photo transistor of FIG. 3 according to anembodiment;

FIG. 12 is a schematic cross-sectional view of a display device having atouch sensor according to an embodiment;

FIG. 13 is a schematic graph obtained by measuring a drain currentaccording to a gate voltage in a photo transistor according to anembodiment;

FIG. 14 is a schematic graph obtained by measuring a drain currentaccording to a gate voltage in a photo transistor according to anembodiment;

FIG. 15 is a schematic graph obtained by measuring a drain currentaccording to a gate voltage in a photo transistor according to anembodiment;

FIG. 16 is a schematic graph obtained by measuring a drain currentaccording to a gate voltage in a photo transistor according to anembodiment; and

FIG. 17 is a schematic graph obtained by measuring a drain current overtime in a photo transistor according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fillyconvey the scope of the invention to those skilled in the art.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

The term “and/or” is intended to include any combination of the terms“and” and “or” for the purpose of its meaning and interpretation. Forexample, “A and/or B” may be understood to mean “A, B, or A and B.” Theterms “and” and “or” may be used in the conjunctive or disjunctive senseand may be understood to be equivalent to “and/or.”

It will also be understood that when a layer is referred to as being“on” another layer or substrate, it can be directly on the other layeror substrate, or intervening layers may also be present. The samereference numbers indicate the same components throughout thespecification.

The term “overlap” may include “layer,” “stack,” “face” or “facing,”“extending over,” “covering” or “partly covering,” or any other suitableterm as would be appreciated and understood by those of ordinary skillin the art. The phrase “not overlap” may include “apart from” or “setaside from” or “offset from” and any other suitable equivalents as wouldbe appreciated and understood by those of ordinary skill in the art.

When an element is referred to as being “in contact” or “contacted” orthe like to another element, the element may be in “electrical contact”and/or in “physical contact” with another element. Further the elementmay be in “indirect contact” or in “direct contact” with anotherelement.

The phrase “at least one of” is intended to include the meaning of “atleast one selected from the group of” for the purpose of its meaning andinterpretation. For example, “at least one of A and B” may be understoodto mean “A, B, or A and B.”

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” may mean within one or morestandard deviations, or within ±30%, 20%, 5% of the stated value.

Unless otherwise defined, all terms used herein (including technical andscientific terms) have the same meaning as commonly understood by thoseskilled in the art to which this disclosure pertains. It will be furtherunderstood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an ideal or excessively formal sense unlessclearly defined in the specification.

Hereinafter, embodiments of the disclosure will be described in detailwith reference to the accompanying drawings.

FIG. 1 is a schematic perspective view illustrating a photo transistoraccording to an embodiment. FIG. 2 is a schematic cross-sectional viewillustrating a photo transistor according to an embodiment.

Referring to FIGS. 1 and 2, a photo transistor 1 according to anembodiment may be included in devices that can be applied as opticalsensors. For example, the photo transistor 1 may be applied to asmartphone, a mobile phone, a tablet PC, a personal digital assistant(PDA), a portable multimedia player (PMP), a television, a game machine,a wristwatch-type electronic device, a head-mounted display, a monitorof a personal computer, a laptop computer, a car navigation system, acar's dashboard, a digital camera, a camcorder, an external billboard,an electronic billboard, a medical device, an inspection device, varioushousehold appliances such as a refrigerator and a washing machine, andthe like.

The photo transistor 1 may serve to sense ambient light and may playvarious roles through light sensing. For example, in a case where thephoto transistor 1 may be applied to a smartphone using an organic lightemitting display device, by using the photo transistor as a lightsensor, the luminance of the organic light emitting display device maybe increased if the luminance of ambient light is high. The luminance ofthe organic light emitting display device may be decreased if theluminance of ambient light is low. Accordingly, visibility may beimproved and power consumption may be reduced.

The photo transistor 1 according to an embodiment may include a gateelectrode 120, a first active layer 140, a second active layer 150, asource electrode 160 and a drain electrode 170 disposed on a substrate110.

The substrate 110 may be an insulating substrate. The substrate 110 mayinclude a transparent material. For example, the substrate 110 mayinclude a transparent insulating material such as glass, polymericmaterial, quartz, or the like, or a combination thereof. For example,the polymeric material may include polyethersulphone (PES), polyacrylate(PA), polyarylate (PAR), polyetherimide (PEI), polyethylene naphthalate(PEN), polyethylene terephthalate (PET), polyphenylene sulfide (PPS),polyallylate, polyimide (PI), polycarbonate (PC), cellulose triacetate(CAT), cellulose acetate propionate (CAP), or a combination thereof. Thesubstrate 110 may be a rigid substrate. However, the substrate 110 isnot limited thereto, and may have a flexible property such that it canbe bent, folded, or rolled. Further, the substrate 110 may include ametal material.

The gate electrode 120 may be disposed on the substrate 110. The gateelectrode 120 may be formed of a single layer or multiple layers. Incase that the gate electrode 120 is a single layer, it may include anyone selected from the group consisting of molybdenum (Mo), aluminum(Al), platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold(Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), titanium(Ti), tantalum (Ta), tungsten (W) and copper (Cu), or an alloy thereof.In case that the gate electrode 120 is a multilayer, it may be amultilayer made of the aforementioned materials. For example, the gateelectrode 120 may be two layers of molybdenum/aluminum-neodymium,molybdenum/aluminum or copper/titanium.

A gate insulating layer 130 covering the gate electrode 120 may bedisposed on the gate electrode 120. The gate insulating layer 130 mayinclude a silicon compound, metal oxide, or the like, or a combinationthereof. For example, the gate insulating layer 130 may include siliconoxide, silicon nitride, silicon oxynitride, aluminum oxide, tantalumoxide, hafnium oxide, zirconium oxide, titanium oxide, or the like, or acombination thereof. In an embodiment, the gate insulating layer 130 mayinclude a SiOx layer.

The first active layer 140 overlapping the gate electrode 120 may bedisposed on the gate insulating layer 130. The first active layer 140may have semiconductor characteristics to act as a substantial channellayer of the transistor. The first active layer 140 may be a lightabsorbing layer capable of absorbing visible light in a specificwavelength band. The first active layer 140 may include an oxidesemiconductor, amorphous silicon, polycrystalline silicon, or atwo-dimensional (2D) material such as graphene or MoS, or a combinationthereof. The oxide semiconductor may include, for example, a binarycompound (ABx), a ternary compound (ABxCy), or a quaternary compound(ABxCyDz) including indium (In), zinc (Zn), gallium (Ga), tin (Sn),titanium (Ti), aluminum (Al), hafnium (Hf), zirconium (Zr), magnesium(Mg) and the like, or a combination thereof. In an embodiment, the firstactive layer 140 may include indium tin zinc oxide (IGZO).

The second active layer 150 may be disposed on the first active layer140. The second active layer 150 may be a layer having a higherphotosensitivity than the first active layer 140. The photosensitivitymay increase as the energy band gap decreases. Therefore, the secondactive layer 150 may have a higher photosensitivity and a smaller energyband gap than the first active layer 140. The second active layer 150may be a light absorbing layer capable of absorbing light in a visiblewavelength band. For example, the second active layer 150 may be a lightabsorbing layer capable of absorbing light in a long wavelength band.The light in a long wavelength band may be light in red and greenwavelength bands. The second active layer 150 may be disposed on (e.g.,directly on) the first active layer 140 and may cover at least a portionof an upper portion of the first active layer 140. The second activelayer 150 may overlap the gate electrode 120 in a same or similar manneras the first active layer 140.

The second active layer 150 may include at least selenium (Se). Forexample, the second active layer 150 may include selenium or a compoundhaving selenium. Selenium may be amorphous selenium or crystallineselenium. For example, the compound having selenium may include a binarycompound (ABx), a ternary compound (ABxCy), or a quaternary compound(ABxCyDz) containing copper (Cu), indium (In), gallium (Ga), or thelike, or a combination thereof. In an embodiment, a single layer ofselenium is described as an example.

The second active layer 150 may have a thickness of about 5 nm to about300 nm. In case that the second active layer 150 has a thickness ofabout 5 nm or more, it may be possible to prevent the photo transistorfrom failing to exhibit its characteristics because the amount ofelectrons passing to the first active layer 140 beyond the band gap ofthe second active layer 150 may be small. In case that the second activelayer 150 has a thickness of about 300 nm or less, it may be possible toprevent an off current of the photo transistor from increasing.

The source electrode 160 and the drain electrode 170 may be disposedbetween the first active layer 140 and the second active layer 150.Specifically, the source electrode 160 may be disposed on a side of thefirst active layer 140 to cover a side of the first active layer 140 andbe disposed below a side of the second active layer 150. The drainelectrode 170 may be disposed on another side of the first active layer140 to cover a side of the first active layer 140 and be disposed belowa side of the second active layer 150.

The source electrode 160 and the drain electrode 170 may be formed of asingle layer or multiple layers. In case that the source electrode 160and the drain electrode 170 are formed of a single layer, it may includeany one selected from the group consisting of molybdenum (Mo), aluminum(Al), platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold(Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), titanium(Ti), tantalum (Ta), tungsten (W) and copper (Cu), or an alloy thereof.In case that the source electrode 160 and the drain electrode 170 areformed of a multilayer, it may consist of two layers of copper/titaniumor molybdenum/aluminum-neodymium, three layerstitanium/aluminum/titanium, molybdenum/aluminum/molybdenum ormolybdenum/aluminum-neodymium/molybdenum.

In the phototransistor 1 according to the above-described embodiment,the first active layer 140 may act as a channel layer of the transistor,and may absorb light in a short wavelength band, e.g., a blue wavelengthband. The second active layer 150 may absorb light in a visiblewavelength band, e.g., red, green and blue wavelength bands. Therefore,by forming the first active layer 140 and the second active layer 150 toabsorb the light (e.g., entire light) in the visible wavelength band, itmay be possible to improve light sensing characteristics.

FIG. 3 is a cross-sectional view illustrating a photo transistoraccording to another embodiment. In FIG. 3, there is a difference in thestack structure of the second active layer, the source electrode and thedrain electrode as compared with the embodiment described with referenceto FIG. 2. In the following description, a description of same orsimilar components as those of FIG. 2 will be simplified or omitted, anda description will be given of different components.

Referring to FIG. 3, the second active layer 150 may be disposed on thefirst active layer 140. The first active layer 140 and the second activelayer 150 may be formed in a same or similar pattern shape. For example,the side edges of the first active layer 140 may be aligned with theside edges of the second active layer 150. Here, “may be aligned” maymean that the side edges of the first active layer 140 and the sideedges of the second active layer 150 extend continuously in contact(e.g., physical contact) with each other.

The source electrode 160 and the drain electrode 170 may be disposed onthe second active layer 150. Specifically, the source electrode 160 maybe disposed on a side of the second active layer 150 to cover a side ofthe second active layer 150 and may be disposed in contact with a sideof the first active layer 140. The drain electrode 170 may be disposedon another side of the second active layer 150 to cover a side of thesecond active layer 150 and may be disposed in contact with a side ofthe first active layer 140.

The difference in structure between the first active layer 140, thesecond active layer 150, the source electrode 160 and the drainelectrode 170 described above with reference to FIGS. 2 and 3 may bedescribed as a difference in the manufacturing process described below.

FIGS. 4 to 8 are schematic cross-sectional views for describing a methodof manufacturing the photo transistor of FIG. 2 according to anembodiment.

Referring to FIG. 4, a gate electrode (e.g., patterned gate electrode)120 may be formed on the substrate 110. The patterned gate electrode 120may be formed by a mask process. For example, after depositing amaterial layer for a gate electrode on the surface (e.g., entiresurface) of the substrate 110, the gate electrode 120 may be formed asshown in FIG. 4 by patterning through a photolithography process.

Referring to FIG. 5, the gate insulating layer 130 may be formed on thesurface (e.g., entire surface) of the substrate 110 on which the gateelectrode 120 may be formed. The first active layer 140 may be formed onthe gate insulating layer 130. The first active layer 140 may be formedby a mask process. For example, a material layer for a first activelayer may be deposited (e.g., entirely deposited) on the gate insulatinglayer 130, and patterned through a photolithography process to form thefirst active layer 140 as illustrated in FIG. 5.

Referring to FIG. 6, a patterned source electrode 160 and a patterneddrain electrode 170 may be formed on the gate insulating layer 130 onwhich the first active layer 140 may be formed. The patterned sourceelectrode 160 and the patterned drain electrode 170 may be formed by amask process. For example, after depositing (e.g., entirely depositing)an electrode material layer on the gate insulating layer 130 on whichthe first active layer 140 may be formed, patterning may be performedthrough a photolithography process to form the source electrode 160 andthe drain electrode 170 as shown in FIG. 6.

Referring to FIG. 7, the second active layer 150 may be formed on thesubstrate 110 on which the source electrode 160 and the drain electrode170 may be formed. The second active layer 150 may be formed by adeposition process using a shadow mask. For example, a shadow mask MSmay be aligned relative to the substrate 110. The shadow mask MS mayinclude an opening OP corresponding to a region in which the secondactive layer 150 is to be formed. An active material (e.g., selenium(Se)) may be deposited on the substrate 110 through the shadow mask MSusing physical vapor deposition (PVD) such as thermal evaporation,e-beam evaporation, sputtering and the like. The deposited activematerial may be deposited in a region (e.g., only in a region)corresponding to the opening OP through the opening OP of the shadowmask MS, thereby forming the second active layer 150 without performinga separate patterning process. Since physical vapor deposition may beperformed at a low temperature, the photo transistor may be manufacturedat a low temperature and applied to various devices requiring a lowtemperature process. Accordingly, the second active layer 150 as shownin FIG. 8 may be formed.

FIGS. 9 to 11 are schematic cross-sectional views for describing amethod of manufacturing the photo transistor of FIG. 3 according to anembodiment. In the following description, a description of same orsimilar components as those of the above-described embodiment will beomitted or simplified to avoid redundancy, and differences will bedescribed.

Referring to FIG. 9, a process until the formation of the patterned gateelectrode 120 and the gate insulating layer 130 on the substrate 110 maybe the same as or similar to the embodiment of FIGS. 4 and 5. A materiallayer 141 for the first active layer and a material layer 151 for thesecond active layer may be sequentially stacked on the surface (e.g.,entire surface) of the substrate 110 on which the gate insulating layer130 may be formed. A photoresist layer may be coated on the materiallayer 151 for the second active layer, and a photoresist pattern PR maybe formed through exposure and development. The photoresist pattern PRmay be overlappingly disposed on a region where the first active layer140 and the second active layer 150 are to be formed.

Referring to FIG. 10, the material layer 141 for the first active layerand the material layer 151 for the second active layer may besequentially etched using the photoresist pattern PR as an etching mask.Thereafter, the photoresist pattern PR may be removed by a strip orashing process, thereby forming the first active layer 140 and thesecond active layer 150 sequentially stacked on the gate insulatinglayer 130. In an embodiment, a case where the photoresist pattern PR maybe used as an etching mask until the patterning of the first activelayer 140 and the second active layer 150 has been illustrated as anexample. However, a patterned upper layer may be used as a hard mask foretching a lower layer. In addition to the hard mask, the photoresistpattern may be used as an etching mask together with the hard mask. Asanother example, after forming the hard mask, the photoresist patternmay be removed, and the lower layer may be etched using the hard mask asan etching mask.

Through the above-described process, the first active layer 140 and thesecond active layer 150 may be formed in a same or similar patternshape. For example, side edges of the first active layer 140 may bealigned with side edges of the second active layer 150. For example,side edges of the first active layer 140 and side edges of the secondactive layer 150 may extend in contact with each other.

Referring to FIG. 11, the patterned source electrode 160 and thepatterned drain electrode 170 may be formed on the gate insulating layer130 on which the second active layer 150 may be formed. The patternedsource electrode 160 and the patterned drain electrode 170 may be formedby a mask process. For example, after depositing (e.g., entirelydepositing) an electrode material layer on the gate insulating layer 130on which the second active layer 150 may be formed, patterning may beperformed through a photolithography process to form the sourceelectrode 160 and the drain electrode 170 as shown in FIG. 11.

The photo transistor according to the embodiments described above mayserve as an optical sensor capable of absorbing most of the light in thevisible wavelength band by forming the first active layer includingmetal oxide and the second active layer including selenium.

Hereinafter, a display device including the photo transistor accordingto an embodiment will be described with reference to FIG. 12. In FIG.12, an organic light emitting display device having a touch sensorembedded therein is illustrated as an example, and a cross-sectionalview of a pixel of the organic light emitting display device isillustrated to describe an example of applying the above-described phototransistor.

FIG. 12 is a schematic cross-sectional view of a display device having atouch sensor embedded therein according to an embodiment.

Referring to FIG. 12, a display part DISL including a first buffer layerBF1, a thin film transistor layer TFTL, a light emitting element layerEML, and a thin film encapsulation layer TFEL may be formed on thesubstrate 110. The thin film transistor layer TFTL may include thin filmtransistors T1 and T2, the gate insulating layer 130, and aplanarization layer PLL.

The first buffer layer BF1 may be disposed on one surface of thesubstrate 110. The first buffer layer BF1 may be formed to protect thethin film transistors T1 and T2 and an organic light emitting layer 172of the light emitting element layer EML from moisture permeation orimpurities of the substrate 110. The first buffer layer BF1 may beformed of inorganic layers that may be alternately stacked on eachother. For example, the first buffer layer BF1 may be formed of multiplelayers in which one or more inorganic layers of a silicon nitride layer,a silicon oxynitride layer, a silicon oxide layer, a titanium oxidelayer and an aluminum oxide layer may be alternately stacked on eachother. The first buffer layer BF1 may be omitted.

The thin film transistor layer TFTL including the thin film transistorsT1 and T2 may be disposed on the first buffer layer BF1. The thin filmtransistors may include a first transistor T1 and a second transistorT2. The first transistor T1 may be a photo transistor according to theabove-described embodiments, and the second transistor T2 may be adriving transistor for driving the light emitting element layer EML.

The first transistor T1 may include a first gate electrode 120 a, afirst active layer 140 a, a second active layer 150, a first sourceelectrode 160 a, and a first drain electrode 170 a. The secondtransistor T2 may include a second gate electrode 120 b, a third activelayer 140 b, a second source electrode 160 b, and a second drainelectrode 170 b.

Specifically, the first gate electrode 120 a and the second gateelectrode 120 b may be disposed on the first buffer layer BF1. The firstgate electrode 120 a and the second gate electrode 120 b may bepatterned and spaced apart from each other.

The gate insulating layer 130 may be disposed on the substrate 110 onwhich the first gate electrode 120 a and the second gate electrode 120 bmay be disposed. In FIG. 12, a case where the gate insulating layer 130may also be formed in a region other than a region overlapping the firstgate electrode 120 a and the second gate electrode 120 b has beenillustrated, but the disclosure is not limited thereto. For example, thegate insulating layer 130 may be formed only in the region overlappingthe first gate electrode 120 a and the second gate electrode 120 b.

The first active layer 140 a and the third active layer 140 b may bedisposed on the gate insulating layer 130. The first active layer 140 amay be disposed to overlap the first gate electrode 120 a, and the thirdactive layer 140 b may be disposed to overlap the second gate electrode120 b. The first active layer 140 a and the third active layer 140 b mayinclude an oxide semiconductor. For example, the oxide semiconductor mayinclude a binary compound (ABx), a ternary compound (ABxCy), or aquaternary compound (ABxCyDz) including indium, zinc, gallium, tin,titanium, aluminum, hafnium (Hf), zirconium (Zr), magnesium (Mg) and thelike, or a combination thereof. For example, the first active layer 140a and the second active layer 140 b may include IGZO (an oxide includingindium, gallium, and tin).

The first source electrode 160 a and the first drain electrode 170 a maybe disposed on the first active layer 140 a. The second source electrode160 b and the second drain electrode 170 b may be disposed on the thirdactive layer 140 b. The second active layer 150 may be disposed on thefirst active layer 140 a, the first source electrode 160 a, and thefirst drain electrode 170 a. Accordingly, the first transistor T1 mayinclude the first gate electrode 120 a, the first active layer 140 a,the second active layer 150, the first source electrode 160 a, and thefirst drain electrode 170 a. The second transistor T2 may include thesecond gate electrode 120 a, the third active layer 140 b, the secondsource electrode 160 b, and the second drain electrode 170 b.

The planarization layer PLL may be disposed on the substrate 110 onwhich the first transistor T1 and the second transistor T2 may bedisposed to planarize a level difference caused by the transistors T1and T2. The planarization layer PLL may be formed of an organic layersuch as acryl resin, epoxy resin, phenolic resin, polyamide resin,polyimide resin and the like, or a combination thereof.

The light emitting element layer EML may be disposed on the thin filmtransistor layer TFTL. The light emitting element layer EML may includelight emitting elements 175 and a pixel defining layer 180. The lightemitting elements 175 and the pixel defining layer 180 may be disposedon the planarization layer PLL. Each of the light emitting elements 175may include a first electrode 171, an organic light emitting layer 172,and a second electrode 173.

The first electrode 171 may be disposed on the planarization layer PLLand may be a pixel electrode. In FIG. 12, a case where the firstelectrode 171 may be electrically connected to the second drainelectrode 170 b of the second transistor T2 through a via hole VIApassing through the planarization layer PLL has been illustrated as anexample, but the disclosure is not limited thereto. As another example,the first electrode 171 may be electrically connected to the secondsource electrode 160 b of the second transistor T2 through the via holeVIA passing through the planarization layer PLL.

In a top emission structure in which light may be emitted toward thesecond electrode 173 viewed with respect to the organic light emittinglayer 172, the first electrode 171 may include a metal material having ahigh reflectivity to have, e.g., a stacked structure (Ti/Al/Ti) ofaluminum and titanium, a stacked structure (ITO/Al/ITO) of aluminum andITO, an APC alloy, and a stacked structure (ITO/APC/ITO) of an APC alloyand ITO. The APC alloy may be an alloy of silver (Ag), palladium (Pd)and copper (Cu). In another example, the first electrode 171 may beformed of a single layer of molybdenum (Mo), titanium (Ti), copper (Cu),or aluminum (Al), or a combination thereof.

In a bottom emission structure in which light may be emitted toward thefirst electrode 171 viewed with respect to the organic light emittinglayer 172, the first electrode 171 may include a transparent conductivematerial (TCO) such as ITO or IZO capable of transmitting light, or asemi-transmissive conductive material such as magnesium (Mg), silver(Ag), or an alloy of magnesium (Mg) and silver (Ag), or a combinationthereof. In case that the first electrode 171 may be formed of asemi-transmissive metal material, the light emission efficiency can beincreased due to a micro-cavity effect.

The pixel defining layer 180 may be disposed to partition the firstelectrode 171 on the planarization layer PLL to serve as a pixeldefining layer defining a light emission region R. The pixel defininglayer 180 may cover an edge of the first electrode 171. The pixeldefining layer 180 may include an organic layer such as acryl resin,epoxy resin, phenolic resin, polyamide resin, polyimide resin and thelike, or a combination thereof.

The light emission region R may refer to a region where the firstelectrode 171, the organic light emitting layer 172 and the secondelectrode 173 may be stacked sequentially and holes from the firstelectrode 171 and electrons from the second electrode 173 may be coupledto each other in the organic light emitting layer 172 to emit light.

The organic light emitting layer 172 may be disposed on the firstelectrode 171 and the pixel defining layer 180. The organic lightemitting layer 172 may include an organic material to emit light in acolor. For example, the organic light emitting layer 172 may include ahole transporting layer, an organic material layer, and an electrontransporting layer. In another example, the organic light emittinglayers 172 of the light emission region R may be formed as one layer toemit white light, ultraviolet light, or blue light.

The second electrode 173 may be disposed on the organic light emittinglayer 172. The second electrode 173 may cover the organic light emittinglayer 172. The second electrode 173 may be a common layer formedcommonly to the pixels. In the top emission structure, the secondelectrode 173 may include a transparent conductive material (TCO) suchas ITO or IZO capable of transmitting light or a semi-transmissiveconductive material such as magnesium (Mg), silver (Ag), or an alloy ofmagnesium (Mg) and silver (Ag). In case that the second electrode 173may be formed of a semi-transmissive metal material, the light emissionefficiency can be increased due to a micro-cavity effect.

In the bottom emission structure, the second electrode 173 may be formedof a metal material, having high reflectivity, such as a stackedstructure (Ti/Al/Ti) of aluminum (Al) and titanium (Ti), a stackedstructure (ITO/Al/ITO) of Al and ITO, an APC alloy, a stacked structure(ITO/APC/ITO) of an APC alloy and ITO, or the like. The APC alloy may bean alloy of silver (Ag), palladium (Pd) and copper (Cu). In anotherexample, the second electrode 173 may be formed of a single layer ofmolybdenum (Mo), titanium (Ti), copper (Cu), aluminum (Al), or ITO, or acombination thereof.

The thin film encapsulation layer TFEL may be disposed on the lightemitting element layer EML. The thin film encapsulation layer TFEL maybe disposed on the second electrode 173. The thin film encapsulationlayer TFEL may include at least one inorganic layer to prevent oxygen ormoisture from penetrating into the organic light emitting layer 172 andthe second electrode 173. The thin film encapsulation layer TFEL mayinclude at least one organic layer to protect the light emitting elementlayer EML from foreign substances such as dust. For example, the thinfilm encapsulation layer TFEL may include a first inorganic layerdisposed on the second electrode 173, an organic layer disposed on thefirst inorganic layer, and a second inorganic layer disposed on theorganic layer. The first inorganic layer and the second inorganic layermay be formed of a silicon nitride layer, a silicon oxynitride layer, asilicon oxide layer, a titanium oxide layer, an aluminum oxide layer, ora combination thereof, but are not limited thereto. The organic layermay include acryl resin, epoxy resin, phenolic resin, polyamide resin,polyimide resin, or the like, or a combination thereof, but is notlimited thereto.

A touch sensor SENL may be disposed on the thin film encapsulation layerTFEL. The touch sensor SENL may include driving electrodes TE, sensingelectrodes RE, and connection parts BE1.

A second buffer layer BF2 may be disposed on the thin film encapsulationlayer TFEL. The second buffer layer BF2 may be formed of multiple layersin which one or more inorganic layers of a silicon nitride layer, asilicon oxynitride layer, a silicon oxide layer, a titanium oxide layerand an aluminum oxide layer may be alternately stacked on each other.

The connection parts BE1 may be disposed on the second buffer layer BF2.The connection parts BE1 may be formed to have, e.g., a stackedstructure (Ti/Al/Ti) of aluminum (Al) and titanium (Ti), a stackedstructure (ITO/Al/ITO) of Al and ITO, an APC alloy, or a stackedstructure (ITO/APC/ITO) of an APC alloy and ITO, but are not limitedthereto. For example, the connection parts BE1 may be formed of a singlelayer of molybdenum (Mo), titanium (Ti), copper (Cu), aluminum (Al), orITO, or a combination thereof.

A first sensing insulating layer TINS1 may be disposed on the connectionparts BE1. The first sensing insulating layer TINS1 may be formed of aninorganic layer, for example, a silicon nitride layer, a siliconoxynitride layer, a silicon oxide layer, a titanium oxide layer, or analuminum oxide layer, or a combination thereof. In another example, thefirst sensing insulating layer TINS1 may be formed of an organic layersuch as acryl resin, epoxy resin, phenolic resin, polyamide resin,polyimide resin and the like, or a combination thereof.

The driving electrodes TE and the sensing electrodes RE may be disposedon the first sensing insulating layer TINS1. The driving electrodes TEand the sensing electrodes RE may be formed to have, e.g., a stackedstructure (Ti/Al/Ti) of aluminum (Al) and titanium (Ti), a stackedstructure (ITO/Al/ITO) of Al and ITO, an APC alloy, or a stackedstructure (ITO/APC/ITO) of an APC alloy and ITO, but are not limitedthereto. For example, the driving electrodes TE and the sensingelectrodes RE may be formed of a single layer of molybdenum (Mo),titanium (Ti), copper (Cu), aluminum (Al), or ITO, or a combinationthereof. The driving electrodes TE and the sensing electrodes RE may beformed of a same material on a same layer.

First contact holes CNT1 may be disposed in the first sensing insulatinglayer TINS1 to expose the connection parts BE1 through the first sensinginsulating layer TINS1. The driving electrodes TE may be electricallyconnected to the connection parts BE1 through the first contact holesCNT1.

A second sensing insulating layer TINS2 may be disposed on the drivingelectrodes TE and the sensing electrodes RE. The second sensinginsulating layer TINS2 may serve to planarize a level difference causedby the driving electrodes TE, the sensing electrodes RE, and theconnection parts BE1. The second sensing insulating layer TINS2 mayinclude an organic layer such as acryl resin, epoxy resin, phenolicresin, polyamide resin, polyimide resin and the like, or a combinationthereof.

The connection parts BE1 electrically connecting the adjacent drivingelectrodes TE may be disposed on the second buffer layer BF2, and thedriving electrodes TE and the sensing electrodes RE may be disposed onthe first sensing insulating layer TINS1. Therefore, the drivingelectrodes TE and the sensing electrodes RE may be electrically isolatedat their intersections, the sensing electrodes RE may be electricallyconnected in a direction, and the driving electrodes TE may beelectrically connected in another intersecting direction.

The first transistor T1 may be a photo transistor according to theabove-described embodiments. The photo transistor can sense light byabsorbing incident light. To this end, a transmissive region TR throughwhich light can be transmitted may be provided on the substrate 110, andthe first transistor T1 may be disposed to overlap the transmissiveregion TR. The transmissive region TR may overlap transparent layersthrough which light can be transmitted, and layers from which light canbe reflected may not be disposed in the transmissive region TR. Forexample, the first transistor T1 may not overlap the first electrode 171of the light emitting element layer EML, and may not overlap theelectrodes RE and TE and the connection part BE1 of the touch sensorSENL.

In an embodiment, by providing the photo transistor in the pixel of theorganic light emitting display device, since it may be not necessary toprovide a separate photo transistor outside the display device (e.g., ina bezel), the bezel can be reduced.

Hereinafter, light absorption characteristics of the photo transistoraccording to the above-described embodiments will be described. In thefollowing description, a photo transistor according to the embodimentshown in FIG. 2 will be described as an example (“embodiment”), and aphoto transistor having a structure in which the second active layer maybe omitted from the structure of FIG. 2 will be described as acomparative example (“comparative embodiment”).

EXAMPLE

A photo transistor according to the embodiment shown in FIG. 2 describedabove was manufactured. The first active layer was formed as a singlelayer of IGZO with a thickness of about 150 nm, and the second activelayer was formed as a single layer of selenium with a thickness of about150 nm.

Comparative Example

A photo transistor was manufactured under the same conditions as in theabove-described embodiment without having the second active layer.

A drain current according to a gate voltage was measured in a state inwhich red light and green light with various intensities wererespectively irradiated to the photo transistors manufactured accordingto the above-described Example and Comparative Example.

FIG. 13 is a schematic graph obtained by measuring a drain currentaccording to a gate voltage after irradiating green light to a phototransistor according to an embodiment. FIG. 14 is a schematic graphobtained by measuring a drain current according to a gate voltage afterirradiating red light to a photo transistor according to a comparativeembodiment. Here, light having a wavelength of about 532 nm and energyof about 2.33 eV was used as the green light.

Referring to FIG. 13, in case that red light was not irradiated to thephoto transistor according to the embodiment, a change of the draincurrent according to the gate voltage was hardly seen. In case thatgreen light with intensities of about 1 mW/mm², about 5 mW/mm² and about10 mW/mm² was irradiated to the photo transistor according to theembodiment, it was exhibited that the drain current according to thegate voltage gradually increases. It exhibited approximately 10⁹ timesdifference in drain current in case that green light was not irradiatedand in case that green light was irradiated at an intensity of about 10mW/mm² at a gate voltage of about −10V. Further, a gate-on voltagevariation in case that green light was not irradiated and green lightwas irradiated was about 26 V. In case that green light was irradiatedto the photo transistor of the embodiment, a threshold voltage moved ina negative direction, and an off current greatly increased.

On the other hand, referring to FIG. 14, in case that green light wasnot irradiated to the photo transistor according to the comparativeembodiment, a change of the drain current according to the gate voltagewas hardly seen. In case that green light with intensities of about 1mW/mm², about 5 mW/mm² and about 10 mW/mm² was irradiated to the phototransistor according to the comparative embodiment, it was exhibitedthat the drain current according to the gate voltage slightly increases.Further, a gate-on voltage variation in case that green light was notirradiated and green light was irradiated was about 4 V. In case thatgreen light was irradiated to the photo transistor of the comparativeembodiment, a threshold voltage slightly moved in the negativedirection, and the off current did not change.

The photoresponsibity, photosensitivity and detectivity, which may becharacteristics of the photo transistors according to the embodiment andthe comparative embodiment, for green light, were measured andrepresented in Table 1 below.

TABLE 1 Photoresponsibity Detectivity (A/W) Photosensitivity (jones)Example 1649.17 7.76 × 10⁹ 5.86 × 10¹³ Comparative 131.11 6.10 × 10⁴1.14 × 10⁹  Example

Referring to Table 1, it can be seen that the photo transistor accordingto the embodiment has significantly higher values in photoresponsibity,photosensitivity and detectivity than the photo transistor according tothe comparative embodiment.

Accordingly, it can be seen that the photo transistor according to theembodiment having the first active layer and the second active layerabsorbs green light to operate as a transistor, but the photo transistoraccording to the comparative embodiment hardly absorbs green light andthus cannot operate as a transistor.

FIG. 15 is a schematic graph obtained by measuring a drain currentaccording to a gate voltage after irradiating red light to a phototransistor according to the embodiment. FIG. 16 is a schematic graphobtained by measuring a drain current according to a gate voltage afterirradiating red light to a photo transistor according to the comparativeembodiment. Here, light having a wavelength of 635 nm and energy of 1.95eV was used as the red light.

Referring to FIG. 15, in case that red light was not irradiated to thephoto transistor according to the embodiment, a change of the draincurrent according to the gate voltage was hardly seen. In case that redlight with intensities of about 1 mW/mm², about 5 mW/mm² and about 10mW/mm² was irradiated to the photo transistor according to theembodiment, it was exhibited that the drain current according to thegate voltage gradually increases. It exhibited approximately 10⁸ timesdifference in drain current in case that red light was not irradiatedand in case that red light was irradiated at an intensity of about 10mW/mm² at a gate voltage of about −10V. Further, a gate-on voltagevariation in case that red light was not irradiated and red light wasirradiated was about 16.6 V. In case that red light was irradiated tothe photo transistor of the embodiment, a threshold voltage moved in thenegative direction.

On the other hand, referring to FIG. 16, in case that red light was notirradiated to the photo transistor according to the comparativeembodiment, a change of the drain current according to the gate voltagewas hardly seen. In case that red light with intensities of about 1mW/mm², about 5 mW/mm² and about 10 mW/mm² was irradiated to the phototransistor according to the comparative embodiment, it was exhibitedthat the drain current according to the gate voltage slightly increases.Further, a gate-on voltage variation in case that red light was notirradiated and red light was irradiated did not appear. Even in casethat red light was irradiated to the photo transistor of the comparativeembodiment, there was no change in the threshold voltage or off current.

The photoresponsibity, photosensitivity and detectivity, which may becharacteristics of the photo transistors according to embodiment andcomparative embodiment, for red light, were measured and represented inTable 2 below.

TABLE 2 Photoresponsibity Detectivity (A/W) Photosensitivity (jones)Example 303.12 6.86 × 10⁸ 5.18 × 10¹² Comparative 83.28 1.57 × 10² 4.03× 10⁷  Example

Referring to Table 1, it can be seen that the photo transistor accordingto the embodiment has significantly higher values in photoresponsibity,photosensitivity and detectivity than the photo transistor according tothe comparative embodiment.

Accordingly, it can be seen that the photo transistor according to theembodiment having the first active layer and the second active layerabsorbs red light to operate as a transistor, but the photo transistoraccording to the comparative embodiment does not absorb red light andthus cannot operate as a transistor.

As described with respect to the light absorption characteristics of thephoto transistors according to the embodiment and the comparativeembodiment shown in FIGS. 13 to 16, the photo transistor according tothe comparative embodiment including only the first active layer of IGZOdid not absorb red light. On the other hand, the photo transistoraccording to Example including the second active layer of selenium inaddition to the first active layer of IGZO absorbed green and red light.Therefore, in the photo transistor according to the embodiment, thesecond active layer of selenium provided to supplement the first activelayer of IGZO absorbs green and red light, thereby absorbing light(e.g., all light) in the visible wavelength band and thus improving thecharacteristics of the optical sensor.

FIG. 17 is a schematic graph obtained by measuring a drain current overtime in case of driving the photo transistor according to theembodiment. Here, the photo transistor was driven to turn on/off thegate every 10 seconds in a state in which constant visible light wasirradiated.

Referring to FIG. 17, in the photo transistor according to theembodiment, the drain current value was kept constant in case that thegate may be turned on. Further, a persistent photocurrent (PPC), whichmay be a drain current that occurs between off and on of the gate, wasexhibited. The photo transistor including the single active layer ofIGZO of the above-described comparative embodiment is known to have avery large amount of persistent photocurrent (hatched area on thegraph), but the photo transistor of embodiment exhibited a small amountof persistent photocurrent.

As a result, it can be seen that the photo transistor according to theembodiment maintains a constant drain current value, has a small amountof persistent photocurrent, and thus has excellent characteristics as aphoto transistor.

As described above, the photo transistor according to the embodiment mayinclude a second active layer including selenium in addition to thefirst active layer including metal oxide, thereby absorbing light (e.g.,all light) in the visible wavelength band. Thus, it may be possible toimprove light sensing characteristics. Further, it may be possible toimprove the photoresponsibity, photosensitivity and detectivity of thephoto transistor. The display device according to the embodimentincludes a photo transistor having excellent characteristics, therebyimproving the light sensing characteristics of the display device.

In concluding the detailed description, those skilled in the art willappreciate that many variations and modifications can be made to theembodiments without substantially departing from the principles of theinvention. Therefore, the disclosed embodiments of the invention areused in a generic and descriptive sense only and not for purposes oflimitation.

What is claimed is:
 1. A photo transistor comprising: a gate electrodedisposed on a substrate; a gate insulating layer that electricallyinsulates the gate electrode; a first active layer overlapping the gateelectrode and including metal oxide, the gate insulating layer beingdisposed between the gate electrode and the first active layer; a secondactive layer disposed on the first active layer and including selenium;and a source electrode and a drain electrode respectively electricallyconnected to the second active layer.
 2. The photo transistor of claim1, wherein the first active layer and the second active layer are incontact with each other in a region in which the first active layer andthe second active layer overlap the gate electrode.
 3. The phototransistor of claim 2, wherein the first active layer is disposed closerto the gate electrode than the second active layer.
 4. The phototransistor of claim 1, wherein the source electrode covers a portion ofthe second active layer, and the drain electrode covers another portionof the second active layer.
 5. The photo transistor of claim 4, whereina side edge of the first active layer and a side edge of the secondactive layer are in contact with each other and aligned with each other.6. The photo transistor of claim 1, wherein the source electrode and thedrain electrode are disposed between the first active layer and thesecond active layer.
 7. The photo transistor of claim 1, wherein thefirst active layer includes at least one selected from an oxidesemiconductor, amorphous silicon, polycrystalline silicon, and atwo-dimensional (2D) material.
 8. The photo transistor of claim 7,wherein the oxide semiconductor includes a compound having at least oneselected from the group consisting of indium (In), zinc (Zn), gallium(Ga), tin (Sn), titanium (Ti), aluminum (Al), hafnium (Hf), zirconium(Zr) and magnesium (Mg), and the 2D material includes graphene or MoS.9. The photo transistor of claim 1, wherein the second active layerincludes a compound having at least one of copper (Cu), indium (In), andgallium (Ga).
 10. The photo transistor of claim 1, wherein the secondactive layer has a thickness of about 5 nm to about 300 nm.
 11. Adisplay device comprising: a substrate including a transmissive regionand a light emission region; a transistor layer disposed on thesubstrate and including a first transistor and a second transistor, thefirst transistor including: a gate electrode; a first active layerincluding metal oxide; a second active layer including selenium; andsource and drain electrodes; a light emitting element layer disposed onthe transistor layer and including a first electrode; and a touch sensordisposed on the light emitting element layer and including electrodes.12. The display device of claim 11, wherein the first transistoroverlaps the transmissive region of the substrate, and the secondtransistor overlaps the light emission region of the substrate.
 13. Thedisplay device of claim 12, wherein the first transistor does notoverlap the first electrode of the light emitting element layer and doesnot overlap the electrodes of the touch sensor.
 14. The display deviceof claim 13, wherein the second transistor overlaps the first electrodeof the light emitting element layer and does not overlap the electrodesof the touch sensor.
 15. The display device of claim 11, wherein thelight emitting element layer further includes: a second electrode facingthe first electrode; and an organic light emitting layer disposedbetween the first electrode and the second electrode, wherein the firsttransistor and the second transistor overlap the second electrode. 16.The photo transistor of claim 11, further comprising: a thin filmencapsulation layer disposed between the light emitting element layerand the touch sensor.
 17. The display device of claim 11, wherein theelectrodes of the touch sensor include driving electrodes and sensingelectrodes.
 18. The display device of claim 11, wherein the first activelayer and the second active layer are in contact with each other in aregion in which the first active layer and the second active layeroverlap the gate electrode.
 19. The photo transistor of claim 18,wherein the first active layer is disposed closer to the gate electrodethan the second active layer.
 20. The photo transistor of claim 11,wherein the second active layer includes a compound having at least oneof copper (Cu), indium (In), and gallium (Ga).